In-vehicle noise is composed of a variety of tonal (frequency-related) components and the tonal components play an important role in the improvement of interior vehicle sound quality. Much research has been focused on the suppression of sound pressure level and achieved certain positive effects. However, in some operating conditions, customers still perceive the tonal components and complain about the vehicle quality even the sound pressure level is relatively low. Therefore, a better understanding of how tonal components are perceived is necessary for automotive designers. To do so, psychoacoustics results about human hearing mechanism to tonal components are comprehensively summed in this study: human hearing response to pure tone, two tones and multiple tones. Then, well-controlled testing stimuli were generated and subjective annoyance testing was conducted. The results show agreement with former researchers' findings. Further, the spectral properties of the testing stimuli such as spectral centroid and spectral flatness were calculated and analyzed. Through regression analysis we find that, for multiple tonal components situation, spectral centroid is related well with human hearing response. Finally, based on the results, some basic design principles of tonal in-vehicle noise are proposed.